The present invention relates generally to a fixed volume liquid transfer device and to a method for transferring liquids and, more particularly, to a microdispenser with a piston for applying external pressure to liquid to fill the microdispenser in the process of transferring the liquid.
Metering and transferring of reagents or samples are generally important in conducting diagnostic tests, especially those providing quantitative results. Apparatus or methods that can easily and quickly deliver accurate amounts of fluid or liquid are usually needed to achieve the desired assay performance. There are currently several products designed to serve this purpose. Among them, the Aqua-Cap(trademark) microdispenser from Drummond Scientific Company of Broomall, Pa. is one of the devices suitable for point-of-care testing.
The Aqua-Cap(trademark) microdispenser includes a plunger and a disposable glass capillary tube containing a porous plug located at a preset position. This product is a self-filling device that takes up liquid by capillary action. The liquid volume in the capillary is precisely controlled and maintained by the porous plug, which becomes impermeable to air when wetted. Following the filling process, the microdispenser functions exactly as a syringe in transporting and dispensing the liquid.
Although manual pipeting is not required in using prior art microdispensers such as the Aqua-Cap(trademark) microdispenser, it is sometimes necessary to slant a tube containing a liquid to be transferred to facilitate the capillary filling. This assisting action, however, may not be acceptable in certain situations, particularly when the liquid is biohazardous. To avoid possible contamination caused by accidental spills in these cases, a liquid transfer device to take up a desired amount of liquid effectively without slanting the tube is desirable.
The present invention is a fixed volume liquid transfer device known as a microdispenser used for quantitative delivery of aqueous liquids or fluids in specimen collection, diagnostic testing, environmental monitoring, or other analytical measurements that require simple and rapid liquid transfer in their procedures.
The fixed volume liquid transfer device consists of a microdispenser defined by a tube having a plunger extending into the tube to dispense collected liquid. A porous plug or other volume control device is mounted in the microdispenser at a preset position below the plunger. The plug is formed of a material that becomes impermeable to air when it becomes wet upon contact by the collected liquid. The tube has an open end for the collection of liquids.
The fixed volume liquid transfer device also includes a piston. The piston has a centric hole into which extends the open end of the tube. The piston also includes an eccentric hole. An air plug is mounted in the eccentric hole and has a tip that extends out of the eccentric hole beyond the piston. In a first, static position, the air plug blocks passage of air through the eccentric hole. In a second position of the air plug the eccentric hole is open allowing the passage of air.
To transfer liquid, the microdispenser is inserted open end first into a test tube containing the liquid. The diameter of the piston is approximately the same as that of the test tube. The microdispenser is pushed down into the test tube. Once the piston contacts the liquid and insertion continues, a pumping action occurs which pumps or forces the liquid into the microdispenser through the open end. Air in the tube above the liquid escapes through the porous plug and around the plunger. Thus, capillary migration of liquid relied upon by prior art microdispensers is not used as the driving force in this filling process.
The tube fills with liquid until the liquid contacts the porous plug, wetting the plug and stopping the flow of liquid into the microdispenser tube. As the piston engages the bottom of the test tube, the tip of the air plug also engages the bottom of the test tube moving the air plug to its second position. In the second position of the air plug the eccentric hole in the piston is open and air on both sides of the piston is balanced. The microdispenser is then withdrawn from the test tube and, due to the open eccentric hole in the piston, air pressure across the piston is balanced and a vacuum below the piston is avoided. Thus, backflow of liquid in the microdispenser tube into the test tube is prevented.
The microdispenser is then transported to a test site and the plunger is depressed to dispense the collected liquid into a testing device.